This invention relates to an induction system for an engine and more particularly to an improved high efficiency induction system for a multi-valve engine.
It is well known that it is possible to improve the breathing efficiency of an internal combustion engine by utilizing multiple intake valves. By using a greater number of valves per cylinder, it is possible to increase the flow area in a given space of the engine. For this reason, four valve per cylinder engines are very popular and five valve per cylinder engines, having three intake valves per cylinder, are also becoming very popular. When the number of intake valves is increased beyond two, several problems arise. One of these problems is insuring that the valve placement is such that the valves can open to a maximum height so as to permit good flow into the cylinder and, at the same time, to maintain a small combustion chamber volume so that the compression ratio for the engine can be kept high and so that undue quenching can be reduced. U.S. Pat. No. 4,660,529, now reissued as U.S. Pat. No. 33,787 is an example of how five valves per cylinder may be placed to provide optimum induction efficiency and high compression ratios.
It is an object of this invention to provide an improved five valve per cylinder, cylinder head and induction arrangement that will further improve the efficiency of such engines.
Although the use of multiple intake valves provides good high speed performance, such large valve areas and low flow resistance passages normally employed therewith tend to provide high power and high speed, but may have a torque curve that has too much emphasis on high end performance.
It is, therefore, a still further object of this invention to provide a multiple valve cylinder head and intake port arrangement wherein the induction system is tuned so as to provide a good torque curve throughout the entire engine speed and load ranges.
It is another object of this invention to provide an improved induction system for an engine embodying multiple intake valves, at least three in number, and wherein each intake valve and its associated induction system is tuned to provide optimum induction efficiency at a different speed range so as to improve the overall torque curve.
One problem that is particularly prevalent with three intake valve engines is that the center intake valve (the one furthest from a plane passing through the center of the cylinder bore axis), tends to be masked by the other intake valves and this can reduce the induction efficiency.
It is, therefore, a still further object of this invention to provide an improved induction system and valve placement for a multiple valve, at least three intake valves per cylinder, engine wherein all valves are capable of providing good induction efficiency.
In conjunction with improving engine performance, particularly at the lower speed ranges, it is desirable to promote turbulence in the combustion chamber. One type of turbulence is an action called "tumble". Tumble is a type of swirl which occurs around a horizontal plane that intersects the cylinder bore axis rather than around the cylinder bore axis. That is, the charge that flows into the chamber is directed toward the side of the chamber opposite from the intake valve where it will be deflected downwardly by the cylinder bore and then back across the head of the piston and upwardly on the side where the charge is introduced. With conventional, three intake valve per cylinder engines, the center intake valve is disposed too far from the center of the cylinder bore axis to generate any tumble action.
It is, therefore, a still further object of this invention to provide an improved multi-valve, cylinder head arrangement including three intake valves wherein the center intake valve and its intake port are configured so as to permit the intake charge issuing from it to be directed across the cylinder to the opposite side.
When multiple valve cylinder heads are employed the valve area requires such a large recess in the cylinder head, particularly with five or more valves per cylinder, that squish action is not possible. As a result, it is normally difficult to obtain any significant squish action with conventional five valve per cylinder, cylinder heads.
It is, therefore, a still further object of this invention to provide an improved five valve per cylinder engine wherein squish action can be easily promoted.